I wouldn't really run a power supply for longer than 5 years unless I'm confident of the manufacturer.

I bought a 500W Silverstone Element I'd say more than 3 years ago, and the only problem I've had was the fan giving out. But even that wasn't due to it failing, only due to a piece of silicon getting stuck in it. All it did was overheat and shut off. Fixed the problem, booted back up fine.

I've had that same Silverstone Element go through 3 sets of parts, no problem.